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            <h1 class="post-title">设计模式之结构型-享元模式 (Flyweight)</h1>
            
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                    <i class="iconfont icon-calendar"></i> 发表于 2020-02-16
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                                <a href="/categories/%E8%AE%BE%E8%AE%A1%E6%A8%A1%E5%BC%8F/"> 设计模式</a>
                            
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                                <a href="/categories/%E8%AE%BE%E8%AE%A1%E6%A8%A1%E5%BC%8F/"># 设计模式</a>
                            
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            <p><a href="https://emojipedia.org/backhand-index-pointing-right/" target="_blank" rel="noopener">👉</a><a href="https://github.com/zhaohaihao/java-design-patterns/tree/master/110-Flyweight" target="_blank" rel="noopener"><strong>文章示例代码</strong></a><a href="https://emojipedia.org/backhand-index-pointing-left/" target="_blank" rel="noopener">👈</a></p>
<h1 id="定义"><a href="#定义" class="headerlink" title="定义"></a>定义</h1><blockquote>
<p>运用共享技术有效地支持大量细粒度的对象。</p>
</blockquote>
<p>“享”即共享，“元”指的是元件，也就是小颗粒的东西。“享元”顾名思义就是共享小部件。</p>
<p>很多的系统程序包含大量的对象，但是这些对象绝大多数都是差不多的，除了一些极个别的属性外。</p>
<p>那么也就是说，在一个系统程序中有多个相同对象的时候，我们只需要共享一份就可以了，不必去实例化每一个对象。</p>
<h1 id="内部状态与外部状态"><a href="#内部状态与外部状态" class="headerlink" title="内部状态与外部状态"></a>内部状态与外部状态</h1><p>享元模式是区分内部状态与外部状态的：</p>
<ul>
<li><strong>内部状态：</strong>可以共享，在享元对象的内部，状态不会随着环境改变而改变</li>
<li><strong>外部状态：</strong>不可以共享，在享元对象的外部，状态会随着环境改变而改变</li>
</ul>
<h1 id="场景示例"><a href="#场景示例" class="headerlink" title="场景示例"></a>场景示例</h1><p>笔者这里以衣服为例。将衣服的品牌作为内部属性共享，将衣服的大小、成分、价格作为外部属性使用。</p>
<h2 id="创建衣服类"><a href="#创建衣服类" class="headerlink" title="创建衣服类"></a>创建衣服类</h2><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@author</span> zhh</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@description</span> 衣服类</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@date</span> 2020-02-16 22:36</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">interface</span> <span class="title">Clothes</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="comment">/**</span></span><br><span class="line"><span class="comment">     * 衣服信息</span></span><br><span class="line"><span class="comment">     */</span></span><br><span class="line">    <span class="function"><span class="keyword">void</span> <span class="title">info</span><span class="params">()</span></span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h2 id="创建衬衣类"><a href="#创建衬衣类" class="headerlink" title="创建衬衣类"></a>创建衬衣类</h2><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@author</span> zhh</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@description</span> 衬衣类</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@date</span> 2020-02-16 22:37</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Shirt</span> <span class="keyword">implements</span> <span class="title">Clothes</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="comment">/**</span></span><br><span class="line"><span class="comment">     * 品牌</span></span><br><span class="line"><span class="comment">     */</span></span><br><span class="line">    <span class="keyword">private</span> String brand;</span><br><span class="line"></span><br><span class="line">    <span class="comment">/**</span></span><br><span class="line"><span class="comment">     * 大小</span></span><br><span class="line"><span class="comment">     */</span></span><br><span class="line">    <span class="keyword">private</span> String size;</span><br><span class="line"></span><br><span class="line">    <span class="comment">/**</span></span><br><span class="line"><span class="comment">     * 成分</span></span><br><span class="line"><span class="comment">     */</span></span><br><span class="line">    <span class="keyword">private</span> String component;</span><br><span class="line"></span><br><span class="line">    <span class="comment">/**</span></span><br><span class="line"><span class="comment">     * 价格</span></span><br><span class="line"><span class="comment">     */</span></span><br><span class="line">    <span class="keyword">private</span> String price;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="title">Shirt</span><span class="params">(String brand)</span> </span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.brand = brand;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setSize</span><span class="params">(String size)</span> </span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.size = size;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setComponent</span><span class="params">(String component)</span> </span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.component = component;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setPrice</span><span class="params">(String price)</span> </span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.price = price;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">info</span><span class="params">()</span> </span>&#123;</span><br><span class="line">        System.out.println(String.format(<span class="string">"当前衬衣信息: &#123;品牌: %s, 大小: %s, 成分: %s, 价格: %s&#125;"</span>, brand, size, component, price));</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>在该场景中，笔者将品牌属性作为其内部状态，在对象创建的初期就初始化完成，状态不会随着外部环境变化，可以共享。</p>
<p>而将大小、成分、价格这些属性当做外部状态，通过 <code>setter</code> 方法供外部修改，状态会随外部环境变化，这些属性不能够共享。</p>
<h2 id="创建衬衣工厂类"><a href="#创建衬衣工厂类" class="headerlink" title="创建衬衣工厂类"></a>创建衬衣工厂类</h2><p>享元模式中通常会出现工厂模式，需要创建一个享元工厂来负责维护一个享元池。</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@author</span> zhh</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@description</span> 衣服工厂类</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@date</span> 2020-02-16 22:48</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">ClothesFactory</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> Map&lt;String, Clothes&gt; CLOTHES_MAP = <span class="keyword">new</span> HashMap&lt;String, Clothes&gt;();</span><br><span class="line"></span><br><span class="line">    <span class="comment">/**</span></span><br><span class="line"><span class="comment">     * 获取衬衣</span></span><br><span class="line"><span class="comment">     * <span class="doctag">@param</span> brand 品牌</span></span><br><span class="line"><span class="comment">     * <span class="doctag">@return</span></span></span><br><span class="line"><span class="comment">     */</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> Clothes <span class="title">getShirt</span><span class="params">(String brand)</span> </span>&#123;</span><br><span class="line">        Shirt shirt = (Shirt) CLOTHES_MAP.get(brand);</span><br><span class="line"></span><br><span class="line">        <span class="keyword">if</span> (shirt == <span class="keyword">null</span>) &#123;</span><br><span class="line">            shirt = <span class="keyword">new</span> Shirt(brand);</span><br><span class="line">            CLOTHES_MAP.put(brand, shirt);</span><br><span class="line">            System.out.println(<span class="string">"创建新的品牌衬衣, 品牌为: "</span> + brand);</span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">        <span class="keyword">return</span> shirt;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h2 id="测试类及输出"><a href="#测试类及输出" class="headerlink" title="测试类及输出"></a>测试类及输出</h2><p>方便起见，在该测试类中随机模拟数据。</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@author</span> zhh</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@description</span> 测试类</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@date</span> 2020-02-16 23:04</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Test</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> String[] BRAND = &#123;<span class="string">"YOUNGOR雅戈尔"</span>, <span class="string">"FIRS杉杉"</span>, <span class="string">"ROMON罗蒙"</span>, <span class="string">"Hodo红豆"</span>&#125;;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> String[] SIZE = &#123;<span class="string">"S"</span>, <span class="string">"M"</span>, <span class="string">"L"</span>, <span class="string">"XL"</span>, <span class="string">"XXL"</span>&#125;;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> String[] COMPONENT = &#123;<span class="string">"棉"</span>, <span class="string">"涤纶"</span>, <span class="string">"真丝"</span>&#125;;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> String[] PRICE = &#123; <span class="string">"￥99"</span>, <span class="string">"￥129"</span>, <span class="string">"￥149"</span>, <span class="string">"￥199"</span> &#125;;</span><br><span class="line"></span><br><span class="line">    <span class="comment">/**</span></span><br><span class="line"><span class="comment">     * 随机模拟</span></span><br><span class="line"><span class="comment">     * <span class="doctag">@param</span> strs 随机模拟数组</span></span><br><span class="line"><span class="comment">     * <span class="doctag">@return</span></span></span><br><span class="line"><span class="comment">     */</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> String <span class="title">getRandom</span><span class="params">(String[] strs)</span> </span>&#123;</span><br><span class="line">        <span class="keyword">return</span> strs[<span class="keyword">new</span> Random().nextInt(strs.length)];</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span> </span>&#123;</span><br><span class="line">        <span class="keyword">for</span> (<span class="keyword">int</span> i = <span class="number">0</span>; i &lt; <span class="number">10</span>; i++) &#123;</span><br><span class="line">            Shirt shirt = (Shirt) ClothesFactory.getShirt(getRandom(BRAND));</span><br><span class="line">            shirt.setSize(getRandom(SIZE));</span><br><span class="line">            shirt.setComponent(getRandom(COMPONENT));</span><br><span class="line">            shirt.setPrice(getRandom(PRICE));</span><br><span class="line">            shirt.info();</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>测试类的输出结果如下：</p>
<blockquote>
<p>创建新的品牌衬衣, 品牌为: ROMON罗蒙<br>当前衬衣信息: {品牌: ROMON罗蒙, 大小: M, 成分: 真丝, 价格: ￥129}<br>创建新的品牌衬衣, 品牌为: FIRS杉杉<br>当前衬衣信息: {品牌: FIRS杉杉, 大小: S, 成分: 棉, 价格: ￥199}<br>当前衬衣信息: {品牌: ROMON罗蒙, 大小: M, 成分: 棉, 价格: ￥99}<br>创建新的品牌衬衣, 品牌为: Hodo红豆<br>当前衬衣信息: {品牌: Hodo红豆, 大小: M, 成分: 棉, 价格: ￥99}<br>当前衬衣信息: {品牌: FIRS杉杉, 大小: XL, 成分: 真丝, 价格: ￥99}<br>当前衬衣信息: {品牌: ROMON罗蒙, 大小: XXL, 成分: 真丝, 价格: ￥99}<br>当前衬衣信息: {品牌: Hodo红豆, 大小: M, 成分: 真丝, 价格: ￥99}<br>当前衬衣信息: {品牌: Hodo红豆, 大小: M, 成分: 涤纶, 价格: ￥149}<br>创建新的品牌衬衣, 品牌为: YOUNGOR雅戈尔<br>当前衬衣信息: {品牌: YOUNGOR雅戈尔, 大小: XXL, 成分: 真丝, 价格: ￥129}<br>当前衬衣信息: {品牌: ROMON罗蒙, 大小: XL, 成分: 涤纶, 价格: ￥199}</p>
</blockquote>
<h2 id="类结构图"><a href="#类结构图" class="headerlink" title="类结构图"></a>类结构图</h2><p>以上示例类的结构图如下所示<br><img src="https://oss.zhaohaihao.com/photo/design-patterns/flyweight/flyweight01.png?x-oss-process=style/style01" alt="image.png"></p>
<h1 id="总结"><a href="#总结" class="headerlink" title="总结"></a>总结</h1><h2 id="适用场景"><a href="#适用场景" class="headerlink" title="适用场景"></a>适用场景</h2><ul>
<li>应用于系统底层开发，解决系统性能问题。</li>
<li>系统有大量相似对象，需要缓冲池。</li>
</ul>
<h2 id="优点"><a href="#优点" class="headerlink" title="优点"></a>优点</h2><ul>
<li>共享相同或者相似的细粒度对象，减少对象的创建，降低系统内存，提高效率。</li>
<li>外部状态相对独立，对象可以在不同的环境中被复用。</li>
</ul>
<h2 id="缺点"><a href="#缺点" class="headerlink" title="缺点"></a>缺点</h2><ul>
<li>读取外部状态使得运行时间变长。</li>
<li>内部状态与外部状态分离，使得程序的逻辑复杂化。</li>
</ul>
<h1 id="参考"><a href="#参考" class="headerlink" title="参考"></a>参考</h1><ul>
<li>《Head First 设计模式》</li>
<li>《大话设计模式》</li>
<li><a href="https://zh.wikipedia.org/wiki/%E4%BA%AB%E5%85%83%E6%A8%A1%E5%BC%8F" target="_blank" rel="noopener">维基百科-享元模式</a></li>
<li><a href="https://www.runoob.com/design-pattern/flyweight-pattern.html" target="_blank" rel="noopener">菜鸟教程-享元模式</a></li>
</ul>

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